Process for the production of esters by alcoholysis



3,098,093 Patented July 16, 1963 3,098,093 PROCESS FOR THE PRODUCTION FESTERS BY ALCOHOLYSIS Hugh J. Hagemeyer, Jr., and Howard N. Wright, Jr.,

Longview, Tex., assignors to Eastman Kodak Company,

Rochester, N.Y., a corporation of New Jersey Filed Feb. 6, 1961, Ser.No. 87,200 3 Claims. (Cl. 260-491) This invention relates to thepreparation of esters, and more particularly, to a continuous processfor preparing esters by alcoholysis and continuously recovering theesters from the process.

This invention is particularly concerned with the interchange reactionbetween an ester containing 4 to 16 carbon atoms and an aliphaticalcohol containing 1 to 4 carbon atoms to produce an ester with fewercarbon atoms than that of the original ester.

The general process of alcoholysis, or ester exchange, is well known andis described in the prior art as an equilibrium reaction which canproceed to completion if one of the products can be separated from thereaction mixture.

The usual method for producing methyl or ethyl esters by alcoholysisconsists of heating the alcohol with the ester in the presence of acatalyst. When the reaction reaches equilibrium, the catalyst isneutralized, filtered or destroyed, and the equilibrium mixture isseparated by distillation. Actually, the equilibrium mixture isdifficult to separate into its components and this is often the casewhen excess lower alcohol is employed in the esterexchange reaction. Thelower alcohol and the ester of the lower alcohol usually azectrope andthe separation of the product is thereby complicated.

An object, therefore, of the present invention is to provide acontinuous ester interchange process which results in nearly completeconversion of the alcohol to product ester.

Another object of this invention is an improved ester interchangeprocess for the continuous conversion of of isobutyl isobutyrate tomethyl isobutyrate.

A more specific object of this invention is an improved process forcarrying out the alcoholysis of an ester of the formula:

wherein R and R may be alkyl, cycloalkyl and arylalkyl with an alcoholof the formula R"OH, wherein R" may be methyl, ethyl, isopropyl, propyl,isobutyl and butyl in the presence of an acidic or basic catalyst toproduce an alcohol of the formula:

RCHR'CH OH and an ester of the formula:

RCHR'CO R" Other objects will appear hereinafter.

in accordance with this invention, there is provided a continuousellicient method for producing esters from alcohols and esters by theester exchange reaction with continuous recovery of the product ester.

For the purpose of facilitating a further description of the invention,the ester and alcohol selected for the alcoholysis are refer-red tohereinafter as the reactant ester and the reactant alcoho, respectively.The products of the alcoholysis are referred to as the "product esterand the product alcohol.

Briefly, the process of this invention comprises heating to reaction ina suitable vessel about 1 mole of reactant alcohol and from about 2 to 9moles of reactant ester in the presence of a catalyst until equilibriumis reached and there is provided an equilibrium mixture. The equilibriummixture will comprise product ester, product alcohol, reactant ester,reactant alcohol, and catalyst. Owing to the fact that a relativelylarge amount of reactant ester is employed in the reaction as comparedto the amount of reactant alcohol, substantially all of the reactantalcohol is reacted therewith and there is present in the equilibriummixture a relatively small amount of reactant alcohol.

The reactant alcohols that can be employed in this invention have thestructural formula R0H wherein R" is an alkyl radical having from 1 to 4carbon atoms. Examples of such alcohols include methanol, ethanol,propancl, isopropanol, n-butanol, and isobutanol.

The reactant esters that can be employed in this invention have thestructural formula wherein R is selected from the group consisting ofthe hydrogen atom; ialkyl radicals such as methyl, ethyl, propyl,isopropyl, n-butyl, pentyl, hexyl, heptyl, octyl and nonyl; cycloalkylradicals such as cyclopentyl and cyclohexyl; aryl radicals such asphenyl and methyl phenyl; and arylalkyl radicals such as benzyl andmethyl benzyl; and wherein R is a radical having at least two carbonatoms and can be selected from alkyl radicals having at least two carbonatoms such \as ethyl, propyl, isopropyl, n-butyl, isobutyl, pentyl,hexyl, octyl, heptyl, and nonyl; cycloalkyl radicals such as cyclopentyland cyclohexyl; and rarylalkyl radicals such as benzyl and methylbenzyl. The total carbon atoms present in both R and R is from 3 to 15.

Examples of suitable esters therefore include ethyl acetate, propylacetate, cyclohexyl propionate, ethyl phenyl acetate, benzyl butyratc,prcpyl n-valcrate, octyl n-valerate, amyl n-heptoate, heptyl n-heptoate,oetyl 11- octoatc, ethyl n-octoate, butyl isobutyrate, and ethylnoctoate.

Not all combinations of the above enumerated reactant alcohols andreactant esters can be employed satisfac torily in carrying out thisinvention. In selecting the reactants, it is essential that the reactantester employed have a boiling point higher than the boiling point of thenext highest boiling component of the equilibrium mixture. For example,when ethyl butyrate is employed as a reactant ester propanol cannot beused as the reactant alcohol because the product ester produced (propylbutyrate) has a boiling point higher than ethyl butyrate. An equilibriummixture comprising ethyl butyrate as the excess reactant ester andpropyl butyrate as the product ester cannot be separated satisfactorilyin a continuous separation process to be detailed hereinafter.

Thus, in carrying out the process, the R radical of the reactant esterwill have at least One more carbon atom than does the R" radical of thereactant alcohol.

After the equilibrium mixture has been produced, the catalytic propertyof the catalyst portion of the equilibrium mixture is renderedineffective promptly whereby the high percentage yield of product esterthat has been obtained, is maintained. The equilibrium mixture issubsequently separated into its several components.

Several methods can be used to render the catalytic property of thecatalyst inelfective. Thus, the catalyst can be neutralized by theaddition to the equilibrium mixture of a suitable neutralizing agent.For example, when sulfuric acid is employed as a catalyst, an amount ofa water solution of sodium hydroxide can be added to the equilibriummixture to react with the sulfuric acid to form sodium sulfate which iswater soluble. The sodium sulfate can be subsequently removed from theequilibrium mixture by washing with hot water. Calcium oxide can beadded to equilibrium mixture containing the sulfuric acid catalyst toform a calcium sulfate precipitate which can be removed from theequilibrium mixture by known methods. It is within the skill of thoseversed in the art to determine the amount and type of neutralizing agentto employ for the various types and amounts of catalysts that can beemployed in this invention.

For the purposes of this invention it is preferred to render thecatalyst ineffective by flash distilling from the equilibrium mixturesubstantially all the product ester. The catalyst employed isnon-volatile at the temperature employed for flash distillation andremains as a portion of a residual composition. Such a method ofrendering the catalyst ineffective is adaptable particularly for acontinuous process of ester production to be detailed more fullyhereinafter. It will be apparent that if flash distillation is to beemployed a catalyst that is substantially nonvolatile at the temperatureemployed in effecting the flash distillation must be employed.

Catalysts that can be employed in carrying out the alcoholysis reactionare basic and acid catalysts known in the art. Suitable catalystsinclude sulfuric acid, phosphoric, acid, p-toluene sulfonic acid, ethylsulfuric acid, ethane sulfonic acid, aluminum chloride, zinc chloride,sodium isobutoxide, aluminum isobutoxide, and mixtures of acidic orbasic catalysts. The amount of catalyst employed can be varied and willusually be employed in an amount equal to from about 0.1% to about 5% byweight based on the total weight of the reactants.

For the purposes of this invention, it is important that the reaction beallowed to proceed to equilibrium to provide an equilibrium mixturewhich comprises product ester, product alcohol, reactant ester, reactantalcohol, and catalyst. Immediately upon reaching equilibrium, asubstantial portion of the equilibrium mixture is separated from thecatalyst and subsequently separated into its several components.

This invention will be described hereinafter with respect to acommercially feasible continuous process for preparing the desiredproduct ester. It will be understood, however, that each of thehereinafter described steps can be carried out separately if desired.

In describing the process of this invention, methanol will be referredto as the reactant alcohol and isobutyl isobutyrate as the reactantester. It is to be understood that the reactant alcohols and reactantesters enumerated above can be employed.

Into an alcoholysis reactor or other suitable reaction vessel providedwith a reflux condenser and heating means such, for example as a steamcoil or stream jacket, there are added methanol, isobutyl isobutyrate,and catalyst in the desired amounts. The reaction vesel is heated slowlyuntil reflux begins, usually at a temperature of from about 100 C. toabout 120 C. Heating at reflux temperature is continued untilequilibrium is reached, usually from about 2 hours to 3 hours, and thereis provided an equilibrium mixture. The equilibrium mixture in the reaction vessel will comprise methanol, isobutanol, methylisob utyrateisobutyl isobutyrate and catalyst.

When equilibrium is produced, a fresh supply of methanol and isobutylisobutyrate in substantially stoichometric amounts are addedcontinuously to the reaction vessel. This fresh spply of reactants plusthe amounts of reactants that are recycled (as hereinafter described) tothe reaction vessel will supply the desired mole ratio of reactants tomaintain the reaction. A fresh supply of catalyst is introduced into thereaction vessel when required. The feed rate of the fresh reactants andthe recycled material is controlled so as to maintain a substantiallyconstant volume of liquid in the reaction vessel.

The equilibrium mixture is removed continuously from the base of thereaction vessel and passed into a flash distillation column havingheating means at the base thereof. Substantially all the catalyst and arelatively large amount of excess unreacted isobutyl isobutyrate areseparated in this column from the other components that comprise theequilibrium mixture. Prompt and effective removal of the catalyst fromthe equilibrium mixture is an important and a critical part of thisinvention as here inabove set forth.

The flash distillation column is preferably a baflled type distillationcolumn, and is preferably operated under a reduced pressure of fromabout 10 to 17 inches of mercury. Atmospheric pressure can be employed,if desired. The reduced pressure can be obtained by means of an eductoror other suitable means. A circulating pump is employed to feeddistilalte into the top of the eductor to provide the vacuum. Heatsupplied by the heating means at the base of the column is closelycontrolled within a range of from about 130 C. to 139 C. so as not tochar or decompose any of the components of the equilibrium mixture. Asteam coil is a suitable heat ing means for use here and it has beendetermined that when 30 p.s.i.g. steam is passed through the steam coil,adequate heat is supplied and no charring or decomposition of theseveral components is observed.

Temperature at the top of the distillation column is maintained at about100 C. to 120 C. Reflux ratio can be varied from about 3:1 to 1:1 with aratio of about 1:1 being preferred.

The catalyst and isobutyl isobutyrate are removed together as a residualfraction from the base of the flash distillation column and recycled tothe reaction vessel. The residual fraction will contain minor amounts ofthe other components of the equilibrium mixture. The residual fractionis removed at a sufficient rate so as to maintain a substantiallyconstant volume thereof in the base of the column.

An overhead fraction comprising methanol, isobutanol (product alcohol),methyl isobutyrate (product ester), and isobutyl isobutyrate is removedfrom the top or head of the flash distillation column and is fedcontinuously into a distillation column A where susbtantially all themethanol is removed with a minor proportion of methyl isobutyrate(product ester) as a methanol-methyl isobutyrate azeotrope.

The distillation column A is operated at atmospheric pressure at areflux ratio of from about 10:1 to 6:1 with an 8:1 ratio beingpreferred. Heat is supplied at the base of the column A by means of asteam coil or other suitable means so as to provide a temperature offrom about 60 to 70 C. at the top or head of column A.

A residual fraction from column A comprising essentially methylisobutyrate, isobutanol, and isbutyl isobutyrate is fed into anotherdistillation column B where methyl isobutyrate is separated out andremoved.

Prior to feeding the above residual fraction from column A into columnB, the residual fraction can be passed through a drying column ifdesired; here any water present therein is substantially all removed.Satisfactory drying columns for this purpose are known in the art. Thisstep in the process can be eliminated if anhydrous reactants areemployed and anhydrous conditions are maintained in the system.

The overhead product that is removed in column B comprises from about98% to 100% methyl isobutyrate.

Distillation column B is operated at atmospheric pressure and at areflux ratio of 8:1 to 12:1 with a ratio of 10:1 being preferred. A baseheater is provided in column B similar to that of column A. The baseheater is maintained at a temperature suflicient to provide an overheadtemperature of from about C. to C.

A residual fraction from column B comprising essentially isobutanol andisobutyl isobutyrate is fed into distillation column C where isobutanolis removed as an overhead fraction, recovered and stored. A residualfraction comprising essentially all isobutyl isobutyrate is fed orrecycled to the reaction vessel. Column C is operated at atmosphericpressure and at a reflux ratio of from 12:1 to 8:1 with a ratio of about10:1 being preferred. A base heater is maintained at a temperaturesufiicient to provide an overhead temperature of from about 109 C. to115 C.

For a more complete understanding of this invention reference is made tothe following detailed desecription and drawing, in which the singleFIGURE is a flow sheet showing a preferred method for carrying out theinvention.

Referring now to the single FiGURE of the drawing, there is showndiagrammatically apparatus 10 that can be employed in carrying out theprocess of this invention. The methanol, isobutyl isobutyrate, andcatalyst are charged through feed line 12 into alcoholysis reacto: 14comprising a reaction vessel 16, reflux condenser 18, and steam coil 20.The reactants are heated to reaction temperature by means of the steamcoil 20 until equilibrium is reached.

The equilibrium mixture is withdrawn continuously from the bottom ofreaction vessel 16 by conduit 22 and fed into flash distillation column24 Where it is separated into an overhead fraction and a residualfraction. The residual fraction comprises the catalyst and is recycledby conduit 26 to reaction vessel 16.

The overhead fraction is removed at the top 23 of the column 24 byconduit 30 and passed into fractional distillation column 32 where it isfractionated into an overhead fraction and into a residual fraction. Theoverhead fraction comprises the azeotrope of methanol and methylisobutyrate and is recycled by conduit 34 to reaction vessel 16. Theresidual fraction comprises isobutyl iso .butyrate, isobutanol, andmethyl isobutyrate.

This residual fraction is fed by conduit 36 into drying column 38 wheresubstantially all the water is removed therefrom. Water is removed as a7% Water-93% methyl isobutyrate azeotrope and is recovered in anoverhead product decanter (not shown). As hereinbefore set forth, thiscolumn can be eliminated from the apparatus if substantially anhydrousreactants are employed and anhydrous conditions are maintainedthroughout the system. A residual fraction from the drying column ispassed by conduit 40 into distillation column 42 where an overheadfraction comprising substantially all methyl isobutyrate is removed andrecovered in a suitable container. A residual fraction comprisingisobutanol and isobutyl isobutyrate is passed by conduit 44 intodistillation column 46 where an overhead fraction comprisingsubstantially all isobutanol is removed and recovered in a suitablevessel. A residual fraction comprises substantially all isobutylisobutyrate and is passed or recycled by conduit 48 to reaction vessel16.

It will be understood that the above reaction conditions, separationconditions, and the like are specifically for the preparation of methylisobutyrate from methanol and isob-utyl isobutyrate.

It is well Within the skill of those versed in the art, having thebenefit of the invention herein disclosed, to control the temperature,the pressure and the like of the various reaction vessels and separationcolumns so as to prepare and separate esters prepared from otherreactants hereinbefore mentioned. Consideration must be given to theboiling points of the reactants and to the boiling points of theproducts produced in scheduling the above described separationprocedure.

The examples that follow are illustrative of this invention.

EXAMPLE I About five liters of a mixture comprising methanol, isobutylisobutyrate and sulfuric acid (98%) is prepared. The mole ratio ofmethanol to isobutyl isobutyrate in the mixture is about 1 mole to 3moles. The sulfuric acid is present in the mixture in an amount equal toabout 1% by Weight based on the total weight of the methanol andisobutyl isobutyrate.

The mixture is fed continuously into a 5-liter reaction vessel fittedwith a reflux condenser and a steam jacket heater at a rate of about 1liter per hour for a period of about 5 hours. Heat is applied at thebase of the reaction vessel continuously during the addition of themixture to provide for gentle boiling and reflux thereof. The refluxtemperature varies from about 106 C. to 115 C. Heating under refluxconditions is continued for about 2 /2 hours after all the mixture hadbeen added to provide an equilibrium mixture comprising the reactantsand the products of the reaction.

The equilibrium mixture comprises, by weight, about 1.2% methanol, about24.2% methyl isobutyrate, about 15.6% isobutanol, and about 58% isobutylisobutyrate.

The equilibrium mixture is fed continuously from the reaction vesselinto the bottom of a 6-inch long column packed with inch Berl saddles.The cross-sectional diameter of the column is 1 /2 inches. The column isprovided with a heater at the base thereof. The heater is maintained ata temperature of about 137 C. and the temperature at the top of thecolumn is maintained at a temperature of about 108 C. The equilibriummixture is fractionated into an overhead fraction comprising, by Weight,about 43.7% methyl isobutyrate, 24.1% isobutanol, about 24.7% isobutylisobutyrate, and about 6.7% of a mixture comprising Water and methanol.A residual fraction comprising, by weight, about 7.3% methylisobutyrate, about 6.1% isobutanol, about 85.4% isobutyl isobutyrate,and substantially all the sulfuric acid contained in the originalmixture remains in the base of the column. The base or residual fractionis recycled to the reaction vessel.

The overhead product is distilled to remove the metha- 1101 as a 75%methanol-25% methyl isobutyrate azeotrope and this azeotrope is recycledto the reaction vessel.

The methyl siobutyrate is subsequently recovered by fractionaldistillation in the manner hereinbefore described with reference to thesingle FlGURE of the drawing. About of the methanol is converted tomethyl isobutyrate and about 32.7% of the isobutyl isobutyrate isconverted to methyl isobutyrate.

EXAMPLE H Methyl isobutyrate is produced in a pilot plant to determinethe commercial feasibility of the process of this invention.

Into a 200 gallon stainless steel reaction vessel there are introducedabout 32 pounds of methanol, about 432 pounds of isobutyl isobutyrate,and about 4.5 pounds of 98% sulfuric acid to provide a mixture.

The mixture is heated slowly to reflux temperature (about 85 C. to 100C.) and the mixture refluxed until an equilibrium mixture comprising thereactants and the products of the reaction is produced. The equilibriummixture will comprise, by weight, from 46% to 56% isobutyl isobutyrate,from 24% to 28% methyl isobutyrate, from 18% to 22% isobutanol, andabout 1% sulfuric acid.

The equilibrium mixture is withdrawn continuously from the base of thereaction vessel and substantially stoichometric amounts of methanol andisobutyl isobutyrate are added continuously to the reaction vessel. Thestoichometric amounts of the above reactants plus the products that arerecycled to the reaction vessel will maintain the total feed ratio atabout 3 moles of isobutyl isobutyrate to each mole of methanol.

The equilibrium mixture is withdrawn and fed into the upper portion of aflash distillation column comprising five half baflles. This column is10 feet high and has a cross-sectional diameter of about 20 inches. Thebase temperature of the flash distillation column is maintained at atemperature of about 137 C. and the overhead temperature is about 112 C.The reflux ratio is about 1:1.

The composition of the overhead fraction comprises, by weight, from 3%to methanol, from 34% to 38% methyl isobutyrate, from 30% to 35%isobutanol, and from 25% to 30% isobutyl isobutyrate. The base orresidual fraction comprises, by weight, about 85% isobutyl isobutyrate,about 15% of methyl isobutyrate plus isobutanol, and sulfuric acid. Theresidual fraction is recycled to the reaction vessel.

The overhead fraction is fed into a 12 inch x 30 feet fractionaldistillation column packed with 1 inch Berl saddles. This column isoperated at atmospheric pressure and at a reflux ratio of 8:1. Toptemperature is maintained at about 64 C. The overhead fraction comprisesa 75% methanol-25% methyl isobutyrate azeotrope and is recycled to thereaction vessel.

The residual fraction is fed into an 18 inch x 50 feet fractionaldistillation column packed with l-inch Pall rings. This column isoperated at atmospheric pressure and at a reflux ratio of about 9: 1.Overhead temperature is maintained at about 93 C. The overhead productcomprises substantially methyl isobutyrate which is collected in avessel and stored.

The residual fraction comprises essentially isobutanol and isobutylisobutyrate. The residual fraction is withdrawn and passed into a 12inch x 30 feet fractional distillation column packed with 1 inch Berlsaddles. This column is operated at atmospheric pressure and at a reflux ratio of about :1. Top temperature is maintained at about 107 C.and the overhead product, isobutanol, is recovered and stored. Theresidual fraction which comprises substantially all isobutyl isobutyrateis recycled to the re action vessel.

EXAMPLE III A pilot plant is operated in substantially the same manneras that described in Example II except that 0.90 weight percent ofp-toluene sulfonic acid is used as a catalyst and the temperature of thereaction vessel is maintained at about 90 C. During one 24 hour period,307 pounds of methanol and 1405 pounds of isobutyl isobutyrate areintroduced into the system. The recycled materials maintained the totalratio of reactants at a ratio of about 3 moles of isobutyl isobutyrateto 1 mole of methanol. During this 24 hour period 976 pounds of methylisobutyrate and 677 pounds of isobutanol are produced. Table I belowsets forth the analyses and yields obtained during this period:

Table I Meth- Methyl Isobuisobutyl anol Isobutunol Isobutyratc tyrateComposition o[ Feeds to Al- 6.6 0. 6 2.0 88.1

coholysis Reactor, percent by weight Aleoholysis Reactor Corr po- 2 2822 48 sition, percent by weight Flash Column Overhead 3 38 35 24Composition, percent by weight Flash Column Base Cornpn- 3 5 91 sition,percent by weight Overhead Product from 99 1 Methyl IsobutyrutoSeparation Column, percent by weight Percent yield of methyl isobutyratefrom methanol Percent yield o[ methyl isobutyrate fromisobutyl.isobutyratc Percent yield of isobutunol from isobutylisobutyrate Percent accountability of methanol Iereeut accountability ofisobutyl isobutyrate EXAMPLE IV act-sacs 7 5 95 5 wqoreq isobutanol, and78.5% isobutyl isobutyrate. This mixture contains 0.89 mole of methylisobutyrate. The methanol-methyl isobutyrate azeotrope contained about0.012 mole of methyl isobutyrate and the remaining 0.88 mole of methylisobutyrate is recovered as substantially pure product.

EXAMPLE V Substantially the same process of Example I is used to prepareethyl isobutyrate from 1 mole of ethanol and 5 moles of isobutylisobutyrate. The catalyst employed is p-toluene sulfonic acid in anamount equal to about 2% by weight based on the total weight of theethanol and isobutyl isobutyrate. The equilibrium mixture comprises, byweight, 1.1% ethanol, 9.9% isobutanol, 14% ethyl isobutyrate, and 75%isobutyl isobutyrate. The conversion of ethanol to ethyl isobutyrate isabout 84% and the conversion of isobutyl isobutyrate to ethylisobutyrate is about 18%. The accountability of the reactants is about99%.

EXAMPLE VI Substantially the same process of Example I is used toprepare isopropyl isobutyrate from 1 mole of isopropanol and 5 moles ofisobutyl isobutyrate. Para toluene sulfonic acid in an amount equal toabout 2% by Weight based on the total weight of the isopropanol andisobutyl isobutyrate is employed as a catalyst. The equilibrium mixtureobtained comprises, by weight, 1.9% isopropanol, 7.65% isobutanol, 1167% isopropyl isobutyrate, and 78.8% isobutyl isobutyrate. Theconversion of isopropanel to isopropyl isobutyrate is about 70.5% andthe conversion of the isobutyl isobutyrate to isopropyl isobutyrate isabout 15%. The accountability of the two reactants is about 99.4%.

It will be understood that the above description and drawing areillustrative of the invention and not in limitation thereof.

We claim as our invention:

1. In the method for the continuous production of an ester product, thesteps which comprise (l) continuously introducing into a reaction vesselcontaining a refluxing mixture substantially stoichiometric amounts of(a) isobutyl isobutyrate and (b) an alcohol having the structuralformula wherein R" is an alkyl radical of from 1 to 3 carbon atoms, saidrefluxing mixture being comprised of an equilibrium mixture of isobutylisobutyrate, alcohol (b), an ester interchange catalyst, an esterreaction product, and isobutyl a1- cohol reaction product, saidequilibrium mixture being derived by admixing and heating to reactionfrom 2 to 9 moles of isobutyl isobutyrate, 1 mole of alcohol (b), and anester interchange catalyst,

(2) feeding equilibrium mixture continuously from the the bottom of thereaction vessel into a flash distillation column heated at the basethereof and operating under reduced pressure and at a reflux ratioofabout 3:1 to 1:1 wherein there is provided substantially immediately anoverhead fraction comprised of isobutyl isobutyrate, alcohol (b), esterreaction product, and isobutyl alcohol and a residual fraction comprisedof substantially all the catalyst carried over in the equilibriummixture and isobutyl isobutyrate,

(3) returning to the reaction vessel a continuous stream of the residualfraction at a rate sufiicient to maintain a substantially constantvolume thereof in the base of the flash distillation column,

(4) feeding continuously the overhead fraction into a distillationcolumn A operating at atmospheric pressure and at a reflux ratio of fromabout 10:1 to 6:1 and distilling therefrom an overhead fractioncomprised of an azeotrope of alcohol (1')) and ester reaction productwhereby substantially all alcohol (b) is removed,

(5) feeding continuously a stream of residual fraction sulfuric acidcatalyst substantially stoichiometric amounts of isobutyi isobutyrateand methanol, said equilibrium mixture being comprised (3) returning tothe reaction vessel as a continuous stream the residual fraction at arate sufficient to maintain a substantially constant volume thereof inthe base of the flash distillation column,

comprised of isobutyl isobutyrate, ester reaction 5 (4) feedingcontinuously the overheated fraction into a product, and isobutylalcohol from the base of coldistillation column A operating atatmospheric presumn A into a distillation column B operated at atsureand at a reflux ratio of from about :1 to 6:1 t h i pressure d at areflux ratio of f 12 ;1 and distilling therefrom an overhead fractioncomto 8:1 wherein an overhead product comprising subpriscd of anazeotrope of methanol and methyl isostantially all ester reactionproduct is removed and 10 butyrate whereby Substantially all 11163131101is there is provided a residual fraction comprised submOVfid, Saiddistillation 0011mm A being Operated stantially of isobutyl alcohol andisobutyl isobutyrate, at a head temperatllrfi of from about to -s (6)feeding continuously a stream of residual fraction feeding ContinuouslyStream Of residual fraction f the base f column B into a distillationlcomprised of isobutyl isobutyrate, methyl isobutyrate, umn C operatedat atmospheric pressure d a and isobutyl alcohol from the base of columnA into refiux ratio of from ab t 12:1 t 8;} h i i a distillation columnB operated at atmospheric presbutyl alcohol is substantially all removedas an ove-r- Sure and a reflux ratio of 12:1 to 311 and having headfraction and there is provided a residual frac- (Warhead iempefalufe offrom about K0 tion comprised essentially of isobutyl isobutyrate, andWhereifi an Overhead FY0611ct P E (7) feeding continuously all theresidual fraction from Substantially all methyl isobutyfflifi is removedand column C to the reaction v el, there is provided a residual fractioncomprised sub- 2, In the method f h continuous production f stantiallyof isobutyl alcohol and isobutyl isobutyrate, methyl isobutyrate, thesteps which comprise (6) feeding continuously a stream of residualfraction (1) introducing continuously i reaction vessel from the base ofcolumn B into a distillation column containing a refluxing mixturecomprised of an equi- C opmated at fllmfisphfirk Pressure and a arefillX librium mixture derived by heating to equilibrium an Talia 0ffmm about 1211 i0 311 and at an Overhead admixture of temperature offrom about 100 C. to 115 C. whereabout 3 moles f isobutyl in isobutylalcohol is substantially all removed as an isobutyrate, overheadfraction and there is provided a residual (b) about 1 l of methanol, andfraction comprised essentially of isobutyl isobutyrate,

and (7) feeding substantially all the residual fraction in column C tothe reaction vessel.

3. The method of claim 2 wherein the flash distillation column isoperated at a reflux ratio of 1:1, column A is operated at a refluxratio of 8:], column B is operated at a reflux of 10: 1, and column C isoperated at a reflux ratio of 10:1.

of isobutyl isobutyrate, methanol, isobutyl alcohol, and methylisobutyrate, (2) withdrawing continuously from the bottom of thereaction vessel the equilibrium mixture and feeding it into a flashdistillation column heated at the base thereof at a temperature of fromabout 130 C. to 139 C. and operating under reduced pressure and at areflux ratio of about 3:1 to 1:1 wherein there is provided an overheadfraction comprised of iso- References Cited in the file of this patentUNITED STATES PATENTS butyl isobutyrate, methanol, methyl isobutyrate,and 2, l fin Aug. 29, 1945 isobutyl alcohol and a residual tractioncomprised 2,63 34 Kuhrt Apr. 7, 1953 of substantially all the catalystcarried over in the 2,911,420 Brown et a1 Nov. 3, 1959 equilibriummixture and isobutyl isobutyrate,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,098,093 July 16, 1963 Hugh .I. Hagemeyer, .Ir., et a1,

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 3, line 23, after "ph0sphoric stri-ke out the comma; line 53, for"vesel" read vessel line 64, for "spply" read supply column 4, line 14,for "distilalte" read distillate column 6, line 38, for "siobutyrate"read isobutyrate column 8, line 28, for "11.67%" read ll.6% column 10,line 5, for "overheated" read overhead Signed and sealed this 3rd day ofMarch 1964 (EEAL) ttest: ERNEST W. SWIDER EDWIN L, REYNOLDS AttestingOfficer Ac Ling Commissioner of Patents

1. IN THE METHOD FOR THE CONTINUOUS PRODUCTION OF AN ESTER PRODUCT, THESTEPS WHICH COMPRISE (1) CONTINUOUSLY INTRODUCING INTO A REACTION VESSELCONTAINING A REFLUXING MIXTURE SUBSTANTIALLY STOICHIOMETRIC AMOUNTS OF(A) ISOBUTYL ISOBUTYRATE AND (B) AN ALCOHOL HAVING THE STRUCTURALFORMULA